Search

The chemical homogeneity in all parts of the bone compacta was investigated in 2 human tibiae taken from male cadavers. The ash and nitrogen contents were used as parameters of the chemical homogeneity. Analyses for calcium and phosphorus were performed in addition to characterize the ash content. The mineral components reached their highest levels in the middle of the diaphysis, but the ash contents decline in the directions towards the epiphysis. The distributions of the values for the organic compounds (nitrogen) show a converse pattern. The nitrogen content was highest especially at points where tendons are anchored in the compacta. The ash or mineral content is approximately proportional to the density of the dry bone substance. The chemical composition of the bone compacta can therefore be used to draw conclusions regarding zones that are subject to different functional loads.

The authors experiments (n = 50) and calculation (n = 1000) with human hollow bone revealed physical and chemical data which were compared. It was shown that the physical and chemical properties are different in the diaphysis and epiphysis. These regularities are the consequence of the physical and chemical inhomogenities. These findings can be explained as a mechanism of protection.

There were laid sections in a difference of 1 cm across the condyli femoris of 5 human formalin-fixed femora and was looked for the curvature of the areas of joints at their marks. In comparing with literature was to be seen that corresponding dats failed at the orientation of the bone. Model conceptions used in case of compensation can't be accepted. Exact calculations of the three-dimensional curvature of surface are presumed for taking into account the mechanism of transfer of forces in the knee joint.

A total of five human knee joints fixed in formalin were available from the 1975/76 dissection course at the Anatomical Institute in Rostock. The different joints where loaded while bent at rightangles (Fig. 1). The maximum load varied between 280 and 400 kp. The length reductions at the compression fracture load were between 5.3 and 10.5 mm. The curves shown beyond the fracture region in Fig. 2 result from the reconsolidation of the fractured bone as an additional elastic region. Bone is generally regarded as a completely elastic material. The load range prior to fracture can probably be considered as elastic in the sense defined by Hooke's law; the curves are correspondingly approximately linear. This also applies to our knee joints, which require a system approach.

Three human pelvises were subjected to static loading in the course of the experiments. The values determined for the elasticity modules lie between 2 and 4.5 kp/min2. The values range between 5 and 14 kp/mm2 if only the compacta is considered. The experiments show that the elasticity modules obtained at cross sections through the Os coxae are higher than those for sections through the hip joint and its immediate surroundings. Here the elasticity module reaches the minimum value of 0.77 kp/cm2 (Fig. 1, cross section No.2, Table 3). The highest breaking strain was 1045 kp (Pelvis II). The longitudinal contraction of the three pelvis was 26.6 mm on average. For the mean height of 27.2 cm for the specimens used, this means that the pelvis, as a system (with hip joint) can be reduced in length by about 10% before a fracture occurs under static load conditions.

Four human hip joints which had been fixed informaldehyde taken from human corpses (average age at death: 72 years) were subjected to pressure along defined axes and tested for static strength and elasticity, the hip joint being regarded as a system. The stress-strain curve reveals no definite linearity. The deviations from Hooke's elasticity found in this way have been explained by the fact that not only completely elastic bone, but also plastic components (cartilage of the joint) were tested. The maximum breaking strain, the modulus of elasticity and the elasticity coefficient were also determined. Only about 50% of all fractures observed on the test set-up were diagnosticised radiologically. The parameters which have, in the past, been determined only on models have thus been replaced by experimental results obtained on actual hip joints.

Static compression tests were undertaken on 40 human skulls while still covered by tissue. The compression tests were performed on the median sagittal part of the calotte. It was found that the skull, like the tubular bones, is fully elastic. Dissection revealed considerably more fractures, particularly in the basal region, than were shown on x-ray pictures (50%). With regard to the mechanisms of fracture, Fig. 2 shows that fractures occur only while the last third of the load is being applied. The following parameters were determined: maximum stress upon fracture, strain, elongation, elasticity module and elasticity coefficient.